This invention generally relates to a gas turbine engine, and more particularly to a nacelle assembly for a gas turbine engine.
In an aircraft gas turbine engine, such as a turbofan engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. The hot combustion gases flow downstream through turbine stages which extract energy from the hot combustion gases. A fan supplies air to the compressor.
Combustion gases are discharged from the turbofan engine through a core exhaust nozzle and a quantity of fan air is discharged through an annular fan exhaust nozzle defined at least partially by a nacelle assembly surrounding the core engine. A majority of propulsion thrust is provided by the pressurized fan air which is discharged through the fan exhaust nozzle, while the remaining thrust is provided from the combustion gases discharged through the core exhaust nozzle.
It is known in the field of aircraft gas turbine engines that the performance of a turbofan engine varies during diversified operability conditions experienced by the aircraft. An inlet lip section located at the foremost end of the turbofan nacelle assembly is typically designed to enable operation of the turbofan engine and reduce separation of airflow from the internal surfaces of the inlet lip section during these diversified conditions. For example, the inlet lip section requires a “thick” inlet lip section to support operation of the engine during specific flight conditions, such as crosswind conditions, take-off conditions and the like. Disadvantageously, the “thick” inlet lip section may reduce the efficiency of the turbofan engine during normal cruise conditions of the aircraft, for example. As a result, the maximum diameter of the nacelle assembly is approximately 10-20% larger than required during cruise conditions.
Nacelle assemblies having a variable air inlet are known which alter the shape of the inlet lip section during take-off and landing conditions to reduce the drag experienced by the aircraft. Variable air inlets of this type include a plurality of actuating mechanisms that effectuate the shape change of the inlet lip section. Disadvantageously, the actuating mechanisms are mechanically complex, difficult to incorporate into the nacelle assembly, and provide negative weight penalties. Additionally, these systems have not fully reduced the drag penalties and flow separation problems that occur during aircraft operation.
Accordingly, it is desirable to improve the performance of a turbofan gas turbine engine during diversified conditions to provide a nacelle assembly having a reduced thickness, reduced weight and reduced drag.